Joining of tubes to tube plates

ABSTRACT

This invention relates to the joining of tubes to tube sheets in alignment with bores through the latter. These bores are slightly larger in diameter than the outside diameters of the tubes. An annular filler insert is positioned adjacent the end of the bore in engagement with the end of the tube. When a non-consumable electrode arc weld is made, the insert melts and becomes united with the end of the tube and the tube sheet, the shape and size of the insert being such that the resulting join has a smooth crevice-free contour, between the tube and the tube sheet.

United States Patent Roberts [54] JOINING OF TUBES TO TUBE PLATES [72]Inventor: Daniel Frank Thomas Roberts, Kent, En-

gland [73] Assignee: Foster Wheeler John Brown Boilers Limited, London,England [22] Filed: Feb. 24, 1970 [21] App]. No.: 13,460

[30] Foreign Application Priority Data Feb. 27, 1969 Great Britain..10,5l9/69 [52] US. Cl ..219/137, 29/1574, 29/4721 [51] Int. Cl ..B23k9/10 [58] Field of Search ..29/157.4, 472.1, 471.1, 426;

[56] References Cited UNlTED STATES PATENTS 2,996,600 8/1961 Gardner eta1 2l9/137 1 June 13, 1972 3,496,629 2/1970 Martucci et a1 ..-.....29/l57.4 UX 2,986,454 5/1961 Jewett 165/1 58 3,205,340 9/1965 Gotch..29/157.4 X

1 FOREIGN PATENTS OR APPLICATIONS 1,420,678 1 H1965 France ..2 1 9/1 37Primary Examiner-Carroll B. Dority, Jr. Att0rney-Dowell & Dowell [57]ABSTRACT This invention relates to the joining of tubes to tube sheetsin alignment with bores through the latter. These bores are slightlylarger in diameter than the outside diameters of the tubes. An annularfiller insert is positioned adjacent the end of the bore in engagementwith the end of the tube. When a nonconsumable electrode arc weld ismade, the insert melts and becomes united with the end of the tube andthe tube sheet, the shape and size of the insert being such that theresulting join has a smooth crevice-free contour, between the tube andthe tube sheet.

3 Claims, 2 Drawing Figures P'ATENTEDJUM 1 a 1912 &

A Home JOINING F TUBES T0 TUBE PLATES This invention relates to thejoining of tubes to tube plates or headers by welding, and for the sakeof convenience reference made hereinafter to tube plates includesreference to headers unless the context specifically requires otherwise.

BACKGROUND OF THE INVENTION There are many Ways in which tubes can bewelded to tube plates. However, to obtain a really satisfactory join itis essential to ensure that there are no crevices in the faces of thejoin. Only in this way can one ensure that crevice corrosion does notoccur. I

The internal bore welding torch described in our United Kingdom Pat. No.934,485 can be used to give crevice-free joins between the ends of tubesand short stub tubes formed on or welded to a tube plate. It is verydifiicult, however, to obtain a crevice-free join between the end of atube and the relatively massive tube plate itself because it is verydifficult to obtain even fusion right the way round the weld unless thewelding apparatus and the parts to be welded are of the very highestaccuracy, the latter being something which commercially available tubessimply do not possess.

It is, therefore, an object of this invention to provide a crevice-freejoin between a tube and a tube plate which is relatively simple to makeand which does not require anything like the same stringent requirementsof accuracy to achieve a really satisfactory weld.

THE INVENTION According to the invention there is provided a method ofmaking a welded join between a tube and a tube plate in alignment with abore through the latter, the bore having a diameter slightly larger thanthe outside diameter of the tube, in which an annular filler insert ispositioned in or near the end of the bore in engagement with the end ofthe tube and a weld is made with a non-consumable electrode, the inserthaving a cross-section such that it fuses during welding and becomesunited with the end of the tube and with the tube plate to give a smoothcrevice-free weld contour between the tube and tube plate.

The invention also extends to the joint made by this method.

By correctly choosing the size and/or the shape of the annular fillerinsert one can ensure that there is a sufficient reserve of material sothat during welding a smooth uniform weld contour is given.

The join according to the invention is quite simple and easy to make andno difficult preparation of the end of the tube or of the tube place isrequired. The tube plate need require no preparation other than drillingthe bore, while, if desired, the end of the tube can be slightlychamfered.

Because the insert is small relatively to the tube and tube plate itwill quickly become completely fused and ensure that no crevices areleft between it and the other parts, even though the dimensions of theparts are not highly accurate in size or accurately aligned. If thefiller insert has an overall outside diameter larger than the diameterof the bore in the tube plate, the insert can be made in a number ofannular segments so that these can be inserted through the bore in thetube plate. When the annular segments are reassembled, however, theremust be no gaps between them which are larger than three thirty-secondsinch.

The composition of the filler insert can be chosen so as to reduce andvirtually eliminate hot cracking of the join during welding orembrittlement due to other causes.

The join so prepared according to the invention has the additional andhighly important advantage that the join can be severed and the tuberemoved, replaced and the new tube joined to the plate or header by themethod of the invention. This is of course particularly important inheat exchangers when the tube forms part of a tube bank extendingbetween two tube plates and is not removable except through the bore inthe tube plate. The tube can of course be readily severed from the plateby drilling or other machining method, and a new tube can be joined tothe plates by an internal bore welding technique using a torch such asthe one described in our United Kingdom Pat. No. 934,485. When welding anew tube in place care must be taken, when necessary, to preventcontamination. This can be achieved by providing a controlled atmosphereon the reverse side of the weld to prevent oxidation or contamination byexclusion of the air with an inert shielding gas, a powdered flux ornon-fusable backing rings such as suitably shaped non-recoverableceramic half rings or recoverable copper-tungsten half rings. Thesebacking rings can if desired, be suitably shaped so as to impart adesired profile to the weld surface. In certain cases such as mild andlow alloy steels the insert may have a composition which reducesatmospheric contamination to an acceptable level without requiring inertgas shielding or the use of backing rings.

The join of the invention is made by an internal bore welding techniqueor by an external welding technique.

DESCRIPTION or THE DRAWINGS An embodiment of the invention will now beillustrated, by way of example, with reference to the accompanyingdiagrammatic drawings, in which:

FIG. I is an axial section through a tube and tube plate before making aweld according to the invention; and

FIG. 2 is an axial section through the completed weld.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows in section a tube10 to be joined to a tube plate 12. Through the latter is a bore 14 ofslightly larger diameter than the outside diameter of the tube 10.

Fitted in the end of the bore 14 is an annular filler insert 16. Thismay be of circular cross-sectional shape or another shape which providesadequate pre-shaping of the material of the insert towards the finaldesired smooth weld contour. Preferably, however, it has thecross-sectional shape shown in FIG. I.

As can be seen the insert 16 fits closely within the bore and also theend 18 of the tube has to be chamfered so as to fit closely with theinsert. The accuracy of fitting does not have to be particularly high,however, since the insert 16 has a crosssectional area sufficientlylarge to provide a reserve of materia] which, when melted by the arc,will flow to accommodate small irregularities or misalignments of theaxes of the tube, bore and insert, and to allow for the tolerance in thediameter of the tube.

The insert may, for instance, be formed in a number of parts and theseparts inserted or assembled against the inner face of the tube plate,for example, during assembly of the tubes to the tube plate.

Once the various parts have been assembled as shown in FIG. 1 a weld ismade, for example, with an inert gas shielded internal bore weldingtorch as shown in our United Kingdom Pat. No. 934,485, the reverse side20 of the weld region being covered, for example, with a flux. Duringthe welding the insert 16 becomes completely fused because it is of muchsmaller mass than either the tube 10 or tube plate 12. The insert 16becomes united both to the end of the tube 10 and to the tube plate 12,giving a welded join 22 as shown in FIG. 2.

The resulting join 22 has a smooth contour joining the tube to the plateboth on the internal surface 24 and external surface 26 of the weld. Thejoin is also crevice-free.

The way in which the join 22 is made is quick and simple and the join isexcellent even though there may have been some slight misalignment orinaccuracies in the various parts.

The making of the join is a simple welding operation and in addition,the tube plate has required no special preparation or machining otherthan drilling to form the bore 14 and the end of the tube 10 has beengiven a slight chamfer, a simple operation.

Also as can be seen from FIG. 2 the join 22 can be severed by a drillinserted in the bore 14 and the tube then removed through the bore.After removing from the tube plate excess material of the join 22, a newtube can be welded to the plate in the way described above. This featureis, of course,

- particularly important in connection with heat exchangers where a tubemay fail during use and cannot be replaced in any simple way other thanremoval through the bore 14 in the tube plate. The insert 16 can, ifrequired, be inserted through the bore 14 as a number of annularsegments which are then assembled in situ to complete the insert. Anygaps between assembled segments must not be more than threethirty-seconds inch. In such a case a very considerable excess of weldmetal can be provided and in certain circumstances this may be desired.However, this excess of weld metal is provided at the expense ofsimplicity of assembly.

A latitude of modification, change and substitution is intended in theforegoing disclosure and in some instances some features of theinvention will be employed without a corresponding use of otherfeatures. Accordingly, it is appropriate that the appended claims beconstrued broadly and in a manner consistent with the spirit and scopeof the invention herein.

We claim: 1. A method of making a welded joint between a cylindricaltube having a frusto conical outer surface at one end and a tube sheetor header comprising the steps of:

a. providing a tube sheet with a bore having a diameter slightly largerthan the outside of said tube,

b. positioning an annular filler insert having a frusto conicalinnersurface adjacent one end of said bore, and placing said one end ofsaid tube to be joined to said sheet in engagement with said fillerinsert, said insert having a crosssection such that it will fuse duringthe making of a weld and will become united with said end of said tubeand with said tube sheet to give a smooth crevice-free weld contourbetween said tube and said tube sheet, and

c. making a circumferential weld from within said bore with an inert gasshielded non-consumable electrode electric arc welder which fuses saidinsert and unites it with said end of said tube and with said tube sheetgiving a smooth crevice free weld contour between said tube and saidtube sheet.

2. A method according to claim 1 in which the composition of the fillerinsert is chosen so to avoid hot cracking of said join during weldingand embrittlement of said join.

3. A method according to claim 1 further comprising the step ofproviding a controlled atmosphere around the outside of said fillerinsert and said end of said tube during welding.

1. A method of making a welded joint between a cylindrical tube having afrusto conical outer surface at one end and a tube sheet or headercomprising the steps of: a. providing a tube sheet with a bore having adiameter slightly larger than the outside of said tube, b. positioningan annular filler insert having a frusto conical inner surface adjacentone end of said bore, and placing said one end of said tube to be joinedto said sheet in engagement with said filler insert, said insert havinga cross-section such that it will fuse during the making of a weld andwill become united with said end of said tube and with said tube sheetto give a smooth crevice-free weld contour between said tube and saidtube sheet, and c. making a circumferential weld from within said borewith an inert gas shielded non-consumable electrode electric arc welderwhich fuses said insert and unites it with said end of said tube andwith said tube sheet giving a smooth crevice free weld contour betweensaid tube and said tube sheet.
 2. A method according to claim 1 in whichthe composition of the filler insert is chosen so to avoid hot crackingof said join during welding and embrittlement of said join.
 3. A methodaccording to claim 1 further comprising the step of providing acontrolled atmosphere around the outside of said filler insert and saidend of said tube during welding.